Estimation of current leakage in left and right ventricular conductance volumetry using a dynamic finite element model

Leakage of electric current through cardiac structures surrounding the ventricle is a primary source of error during ventricular volume measurements using a conductance catheter. This error can be represented as a leakage volume, VL. VL is generally estimated by a saline-bolus method, and is assumed constant throughout the cardiac cycle. However, dynamic changes in ventricular volume and cardiac wall thickness could change VL. To estimate VL, a dynamic finite element model of the heart was developed based on MR images. Conductance measurements were simulated using a modeled conductance catheter, and true VL was calculated. VL varied from 22.7 ml (end-systole) to 26.4 ml (end-diastole) in the left ventricle and from 19.9 ml (end-systole) to 26.9 ml (end-diastole) in the right ventricle. The saline-bolus method underestimated VL in both the left (VL = 19.4 ml) and the right (VL = 4.1 ml) ventricular volume measurements. VL increased linearly with the ratio of blood to tissue resistivity, and changed minimally with catheter position. These results indicate that VL has to be estimated dynamically throughout the cardiac cycle to obtain accurate cardiac volume measurements. The results also show that the saline bolus method does not estimate current leakage accurately, especially in the right ventricular volume measurement.

Imaging of cardiac and paracardiac masses

Magnetic resonance imaging (MRI) and computed tomography (CT) are important imaging modalities for the noninvasive characterization of cardiac and paracardiac masses. They are, in general, superior to other modalities (e.g., echocardiography) in their ability to delineate the exact location and the extent of the lesion and to demonstrate the effects of the lesion on surrounding structures. MRI and CT may also be helpful in suggesting a specific diagnosis, because some tumors have rather characteristic locations and appearances. In addition, both modalities can be extremely helpful in both treatment planning and posttreatment follow-up because they are noninvasive, reproducible, and enable detection of residual or recurrent mass.

Validation of real-time three-dimensional echocardiography for quantifying left ventricular volumes in the presence of a left ventricular aneurysm: in vitro and in vivo studies

OBJECTIVES

To validate the accuracy of real-time three-dimensional echocardiography (RT3DE) for quantifying aneurysmal left ventricular (LV) volumes.

BACKGROUND

Conventional two-dimensional echocardiography (2DE) has limitations when applied for quantification of LV volumes in patients with LV aneurysms.

METHODS

Seven aneurysmal balloons, 15 sheep (5 with chronic LV aneurysms and 10 without LV aneurysms) during 60 different hemodynamic conditions and 29 patients (13 with chronic LV aneurysms and 16 with normal LV) underwent RT3DE and 2DE. Electromagnetic flow meters and magnetic resonance imaging (MRI) served as reference standards in the animals and in the patients, respectively. Rotated apical six-plane method with multiplanar Simpson's rule and apical biplane Simpson's rule were used to determine LV volumes by RT3DE and 2DE, respectively.

RESULTS

Both RT3DE and 2DE correlated well with actual volumes for aneurysmal balloons. However, a significantly smaller mean difference (MD) was found between RT3DE and actual volumes (-7 ml for RT3DE vs. 22 ml for 2DE, p = 0.0002). Excellent correlation and agreement between RT3DE and electromagnetic flow meters for LV stroke volumes for animals with aneurysms were observed, while 2DE showed lesser correlation and agreement (r = 0.97, MD = -1.0 ml vs. r = 0.76, MD = 4.4 ml). In patients with LV aneurysms, better correlation and agreement between RT3DE and MRI for LV volumes were obtained (r = 0.99, MD = -28 ml) than between 2DE and MRI (r = 0.91, MD = -49 ml).

CONCLUSIONS

For geometrically asymmetric LVs associated with ventricular aneurysms, RT3DE can accurately quantify LV volumes.

Potency preservation after three-dimensional conformal radiotherapy for prostate cancer: preliminary results

We sought to assess potency preservation after three-dimensional conformal radiotherapy (3D-CRT) in prostate cancer patients eligible for radical prostatectomy, conventional radiotherapy, 3D-CRT, or transperineal prostate implantation. Patients with more advanced disease are commonly treated with hormonal therapy, which can cause impotence, and were consequently excluded from the analysis. Between December 1991 and June 1998, 198 prostate cancer patients were treated with 3D-CRT at the University of California, Davis Medical Center. Fifty-two of these patients had a pretreatment prostate-specific antigen (PSA) level of 10.0 ng/ml or less, a Gleason score of 6 or less, and a 1997 AJCC clinical stage T1bN0M0 to T2bN0M0. One patient was not evaluable. None of the 51 evaluable patients had diabetes mellitus. In 40 patients, the prostate gland only was irradiated to a total dose of 66 to 79.2 Gy by using daily 1.8-Gy fractions. In 11 patients, the prostate and seminal vesicles were treated to 44 to 55.8 Gy. Lymph nodes were not included in the clinical target volume. The median age was 68 years, and the median length of follow-up was 15 months. Potency in this study is defined as an erection sufficient for vaginal penetration. Kaplan-Meier analysis was used to describe potency as a function of time after 3D-CRT. Of the 51 evaluable patients, 35 (69%) were potent, 15 were impotent, and 1 was sexually inactive before 3D-CRT. Kaplan-Meier estimates of the potency preservation rates 1, 2, and 3 years after 3D-CRT are 100%, 83%, and 63%, respectively. On multivariate analysis, age, total radiation dose, and a history of transurethral resection of the prostate did not significantly affect potency preservation rates. Three (43%) of 7 patients who became impotent after 3D-CRT and used sildenafil were subsequently able to achieve erections sufficient for vaginal penetration. The preliminary results reported herein suggest that approximately two thirds of prostate cancer patients will retain their potency 3 years after 3D-CRT. Further follow-up is necessary to assess long-term potency after 3D-CRT. Sildenafil should be considered in patients who develop radiation-induced impotence.

In vitro metabolism of polychlorinated biphenyl congeners by beluga whale (Delphinapterus leucas) and pilot whale (Globicephala melas) and relationship to cytochrome P450 expression

We measured rates of oxidative metabolism of two tetrachlorobiphenyl (TCB) congeners by hepatic microsomes of two marine mammal species, beluga whale and pilot whale, as related to content of selected cytochrome P450 (CYP) forms. Beluga liver microsomes oxidized 3,3',4,4'-TCB at rates averaging 21 and 5 pmol/min per mg for males and females, respectively, while pilot whale samples oxidized this congener at 0.3 pmol/min per mg or less. However, rates of 3,3',4,4'-TCB metabolism correlated with immunodetected CYP1A1 protein content in liver microsomes of both species. The CYP1A inhibitor alpha-naphthoflavone inhibited 3,3',4,4'-TCB metabolism by 40% in beluga, supporting a role for a cetacean CYP1A as a catalyst of this activity. Major metabolites of 3,3',4,4'-TCB generated by beluga liver microsomes were 4-OH-3,3',4',5-TCB and 5-OH-3,3',4,4'-TCB (98% of total), similar to metabolites formed by other species CYP1A1, and suggesting a 4,5-epoxide-TCB intermediate. Liver microsomes of both species metabolized 2,2',5,5'-TCB at rates of 0.2-1.5 pmol/min per mg. Both species also expressed microsomal proteins cross-reactive with antibodies raised against some mammalian CYP2Bs (rabbit; dog), but not others (rat; scup). Whether CYP2B homologues occur and function in cetaceans is uncertain. This study demonstrates that PCBs are metabolized to aqueous-soluble products by cetacean liver enzymes, and that in beluga, rates of metabolism of 3,3',4,4'-TCB are substantially greater than those of 2,2',5,5'-TCB. These directly measured rates generally support the view that PCB metabolism plays a role in shaping the distribution patterns of PCB residues found in cetacean tissue.

Brief report: birth status, medical complications, and social environment: individual differences in development of preterm, very low birth weight infants

OBJECTIVE

To assess whether medical complications mediate the relationship between birth status (i.e., birth weight and gestational age) and developmental outcome of preterm, very low birth weight (VLBW) infants, as well as the role of the early social environment (maternal distress and social support) in infant development.

METHOD

Birth status and medical complication information was collected during the child's NICU stay. Maternal distress was assessed with the Beck Depression Inventory and the Parenting Stress Index at 4 months corrected infant age. Social support was measured with the Dunst Scales at 4 months corrected age. Child development measures were collected at 4 and 13 months corrected age (Bayley MDI and PDI), and at 36 months chronological age (PPVT-R and Achenbach CBCL).

RESULTS

Medical complications mediated the birth status-outcome relationship at 4 and 13 months, but not at 36 months. The 36-month outcomes were predicted by 4-month maternal distress and social support.

CONCLUSIONS

Prematurity and VLBW are indirectly related to early developmental outcome through their association with medical complications. However, by 36 months, developmental outcomes are more closely related to aspects of the early social environment than to early physiological factors.

New digital measurement methods for left ventricular volume using real-time three-dimensional echocardiography: comparison with electromagnetic flow method and magnetic resonance imaging

AIM

The aim of this study was to investigate the feasibility and accuracy of using symmetrically rotated apical long axis planes for the determination of left ventricular (LV) volumes with real-time three-dimensional echocardiography (3DE).

METHODS AND RESULTS

Real-time 3DE was performed in six sheep during 24 haemodynamic conditions with electromagnetic flow measurements (EM), and in 29 patients with magnetic resonance imaging measurements (MRI). LV volumes were calculated by Simpson's rule with five 3DE methods (i.e. apical biplane, four-plane, six-plane, nine-plane (in which the angle between each long axis plane was 90 degrees, 45 degrees, 30 degrees or 20 degrees, respectively) and standard short axis views (SAX)). Real-time 3DE correlated well with EM for LV stroke volumes in animals (r=0.68-0.95) and with MRI for absolute volumes in patients (r-values=0.93-0.98). However, agreement between MRI and apical nine-plane, six-plane, and SAX methods in patients was better than those with apical four-plane and bi-plane methods (mean difference = -15, -18, -13, vs. -31 and -48 ml for end-diastolic volume, respectively, P<0.05).

CONCLUSION

Apically rotated measurement methods of real-time 3DE correlated well with reference standards for calculating LV volumes. Balancing accuracy and required time for these LV volume measurements, the apical six-plane method is recommended for clinical use.

Does intraoperative hetastarch administration increase blood loss and transfusion requirements after cardiac surgery?

Hetastarch is used for intravascular volume expansion in cardiac surgery. Studies show conflicting effects of intraoperative hetastarch administration on postoperative bleeding. Hetastarch was routinely used for volume expansion during cardiovascular surgeries at our institution until its use was discontinued intraoperatively. We performed a retrospective chart review on patients undergoing primary coronary artery bypass grafting, valve repair or replacement requiring cardiopulmonary bypass (n = 444), 234 of which received intraoperative hetastarch and 210 did not. There was no difference in demographics, cardiac surgery, or cardiopulmonary bypass duration between the two groups. Blood loss for 0-4 h postoperatively was 377 +/- 244 mL in the group not receiving hetastarch compared with 515 +/- 336 mL in the group that received hetastarch (P < 0.001). For 0-24 h postoperatively, blood loss was 923 +/- 473 mL versus 1,283 +/- 686 mL in the absence and presence of hetastarch, respectively (P < 0.001). Allogeneic transfusion requirements (cryoprecipitate, fresh frozen plasma, and platelets) were larger in the hetastarch group (all P < 0.001). Nearly all (99%) patients in the hetastarch group received less than the manufacturer's recommended dose (20 mL/kg) of hetastarch.

IMPLICATIONS

Our large retrospective study suggests that intraoperative use of hetastarch in primary cardiac surgery with cardiopulmonary bypass may increase bleeding and transfusion requirements. A large prospective study is needed to determine if intraoperative administration of hetastarch should be avoided during cardiovascular surgery.

Bioimpedance monitoring: better than chest x-ray for predicting abnormal pulmonary fluid?

Bioimpedance monitoring may aid in treating heart failure. Mean thoracic electrical impedance (Zo) is inversely proportional to thoracic fluid volume and may offer greater sensitivity for detecting thoracic fluid. OBJECTIVE. Compare bioimpedance monitoring thoracic fluid detection to that of chest x-ray. METHOD. Prospective convenience sample. SETTING. 1000 bed teaching hospital. PARTICIPANTS. Patients with suspected heart failure and shortness of breath. A single blinded radiologist interpreted chest x-rays as: normal, cardiomegaly, or abnormal pulmonary fluid. STATISTICS. General linear model with post hoc Bon Ferroni pairwise comparisons. RESULTS. 131 patients, mean age 66.8 years, 64.3% male, with an initial mean Zo=18 ohms. There was a significant difference (p<0.0002) between patients with cardiomegaly (Zo=17.5+/-5.5) or abnormal pulmonary fluid on chest x-ray (Zo=17.2+/-4.2) compared to normals (Zo=23.4+/-5.4). There was no difference between cardiomegaly and abnormal pulmonary fluid patients. CONCLUSION. Bioimpedance measurement may detect pulmonary fluid not apparent on chest radiograph. (c)2000 by CHF, Inc.

MR angiography of the thoracic aorta with an electrocardiographically triggered breath-hold contrast-enhanced sequence

An electrocardiographically (ECG) triggered breath-hold contrast material-enhanced magnetic resonance (MR) angiography sequence has been developed for imaging the thoracic aorta. A three-dimensional (3D) gradient-echo sequence is used with a contrast material bolus. Forty-nine patients with various aortic abnormalities and five healthy volunteers underwent imaging with the sequence. All studies were performed in a single breath hold. ECG-triggered breath-hold contrast-enhanced MR angiography was tolerated in 48 of the 49 patients. The images demonstrated no respiratory motion artifacts and diminished pulsation artifacts. The cardiac chambers, aortic root, ascending and descending aorta, aortic arch, proximal arch vessels, and proximal coronary arteries were clearly demonstrated and not obscured by ghost artifacts. The 3D data set allowed excellent multiplanar reformation, permitting orthogonal or oblique views of the vascular anatomy. A variety of congenital and acquired abnormalities were clearly identified. When this sequence is used, it is important to evaluate both the maximum-intensity projection and source images. Delayed imaging should be performed to detect late filling. In conjunction with cine MR and T1-weighted spin-echo imaging, ECG-triggered breath-hold contrast-enhanced MR angiography should be considered the technique of choice for imaging the thoracic aorta.

Nonconservative charged-particle swarms in ac electric fields

A time-dependent multi-term technique has been developed and employed to solve the space- and time-dependent Boltzmann equation for charged-particle swarms in ac electric fields. This technique allows for the accurate calculation of both the full set of transport coefficients and the phase-space distribution function. This technique avoids restrictions on the field amplitude and frequency and/or the charged-particle to neutral molecule mass ratio traditionally associated with many contemporary investigations. To our knowledge, it represents the first rigorous treatment of the explicit effects of nonconservative processes on transport coefficients in ac electric fields. The phenomena associated with these explicit effects of nonconservative processes are striking (e.g., negative phase lags in the drift velocity for an attaching gas), and the errors associated with traditional treatments of ionization and attachment on the transport coefficients are highlighted.

Role of transesophageal echocardiography in assessing diastolic dysfunction in a large clinical practice: a 9-year experience

BACKGROUND

Two-dimensional transthoracic echocardiography with respiratory monitoring has been used to characterize diseases that impair diastolic function. Transesophageal echocardiography (TEE) has emerged as a complementary technique to evaluate patients with these diseases. The purpose of this study was to evaluate in a large clinical practice the utility of TEE with respiratory monitoring for classification of patients with diastolic dysfunction.

METHODS

Over a 9-year period TEE was used to examine 192 patients referred to an echocardiography laboratory for additional evaluation of abnormal diastolic function. We performed pulsed-wave Doppler TEE of the left ventricular inflow and pulmonary veins and respiratory monitoring to categorize patients as showing restrictive physiologic features, constriction with or without effusion, mixed constriction and restriction, abnormal relaxation, pseudonormalization, large pericardial effusion or tamponade, or normal diastolic function.

RESULTS

Patients with diastolic dysfunction underwent 3% of the total number of transesophageal studies conducted during the study period. Among the 192 patients referred for TEE, abnormal diastolic function was found in 181 (94%); 11 (6%) had normal diastolic function. Seventy-one (39%) of the 181 patients had restrictive physiologic features. Constrictive pericarditis was found in 54 (30%) of the patients and was confirmed for all 31 patients who underwent pericardiectomy. Mixed constriction and restriction was present in 21 (12%) of the patients. The other 35 patients (19%) had abnormal relaxation, pseudonormalization, or large pericardial effusion or tamponade. The cause of diastolic dysfunction was idiopathic for 32% of the patients, previous cardiac operation for 26%, cardiac amyloidosis for 23%, radiation therapy for 11%, and hypertension or advanced ischemic heart disease for 8%.

CONCLUSION

Two-dimensional and Doppler TEE with respiratory monitoring is useful in categorizing patients with impaired diastolic function, primarily into those with restrictive physiologic features or constrictive pericarditis.

Initial clinical experience of real-time three-dimensional echocardiography in patients with ischemic and idiopathic dilated cardiomyopathy

The geometry of the left ventricle in patients with cardiomyopathy is often sub-optimal for 2-dimensional ultrasound when assessing left ventricular (LV) function and localized abnormalities such as a ventricular aneurysm. The aim of this study was to report the initial experience of real-time 3-D echocardiography for evaluating patients with cardiomyopathy. A total of 34 patients were evaluated with the real-time 3D method in the operating room (n = 15) and in the echocardiographic laboratory (n = 19). Thirteen of 28 patients with cardiomyopathy and 6 other subjects with normal LV function were evaluated by both real-time 3-D echocardiography and magnetic resonance imaging (MRI) for obtaining LV volumes and ejection fractions for comparison. There were close relations and agreements for LV volumes (r = 0.98, p <0.0001, mean difference = -15 +/- 81 ml) and ejection fractions (r = 0.97, p <0.0001, mean difference = 0.001 +/- 0.04) between the real-time 3D method and MRI when 3 cardiomyopathy cases with marked LV dilatation (LV end-diastolic volume >450 ml by MRI) were excluded. In these 3 patients, 3D echocardiography significantly underestimated the LV volumes due to difficulties with imaging the entire LV in a 60 degrees x 60 degrees pyramidal volume. The new real-time 3D echocardiography is feasible in patients with cardiomyopathy and may provide a faster and lower cost alternative to MRI for evaluating cardiac function in patients.

Biphasic truncated exponential waveform defibrillation

This paper presents data from studies that have compared the efficacies of biphasic truncated exponential (BTE) and monophasic damped sine (MDS) waveform defibrillation in patients with out-of-hospital cardiac arrest and in in-hospital defibrillation. When a shock is delivered, rhythms evolve rapidly in a variety of directions and take different courses, even over a short time. When defibrillation is defined as termination of ventricular fibrillation at 5 seconds postshock, whether to an organized rhythm or asystole, low-energy BTE shocks appear to be more effective than high-energy MDS shocks in out-of-hospital arrest. For future research, the terms associated with defibrillation should be standardized and used uniformly by all investi-gators. In particular, there should be an agreed-upon definition of shock efficacy.

Oxidative inactivation of cytochrome P-450 1A (CYP1A) stimulated by 3,3',4,4'-tetrachlorobiphenyl: production of reactive oxygen by vertebrate CYP1As

Microsomal cytochrome P-450 1A (CYP1A) in a vertebrate model (the teleost fish scup) is inactivated by the aryl hydrocarbon receptor agonist 3,3',4,4'-tetrachlorobiphenyl (TCB). Here, the mechanism of CYP1A inactivation and its relationship to reactive oxygen species (ROS) formation were examined by using liver microsomes from scup and rat and expressed human CYP1As. In vitro inactivation of scup CYP1A activity 7-ethoxyresorufin O-deethylation by TCB was time dependent, NADPH dependent, oxygen dependent, and irreversible. TCB increased microsomal NADPH oxidation rates, and CYP1A inactivation was lessened by adding cytochrome c. CYP1A inactivation was accompanied by loss of spectral P-450, a variable loss of heme and a variable appearance of P-420. Rates of scup liver microsomal metabolism of TCB were < 0.5 pmol/min/mg, 25-fold less than the rate of P-450 loss. Non-heme iron chelators, antioxidant enzymes, and ROS scavengers had no influence on inactivation. Inactivation was accelerated by H(2)O(2) and azide but not by hydroxylamine or aminotriazole. TCB also inactivated rat liver microsomal CYP1A, apparently CYP1A1. Adding TCB to scup or rat liver microsomes containing induced levels of CYP1A, but not control microsomes, stimulated formation of ROS; formation rates correlated with native CYP1A1 content. TCB stimulated ROS formation by baculovirus-expressed human CYP1A1 but not CYP1A2. The results indicate that TCB uncouples the catalytic cycle of CYP1A, ostensibly CYP1A1, resulting in formation of ROS within the active site. These ROS may inactivate CYP1A or escape from the enzyme. ROS formed by CYP1A1 may contribute to the toxicity of planar halogenated aromatic hydrocarbons.

Charged-particle transport in gases in electric and magnetic fields crossed at arbitrary angles: Multiterm solution of Boltzmann's equation

A multiterm solution of the Boltzmann equation has been developed and used to calculate transport coefficients of charged-particle swarms in gases under the influence of electric and magnetic fields crossed at arbitrary angles psi. The hierarchy resulting from a spherical harmonic decomposition of the Boltzmann equation in the hydrodynamic regime [Ness, Phys. Rev. A 47, 327 (1993)] is solved numerically by representing the speed dependence of the phase-space distribution function in terms of an expansion in Sonine polynomials about a weighted sum of Maxwellian distributions at different temperatures. Results are given for charged-particle swarms in certain model gases over a range of psi and field strengths. The variation of the transport coefficients with psi is addressed using physical arguments. The errors associated with the two-term approximation and inadequacies of Legendre polynomial expansions are highlighted.

Electrocardiographic evaluation of defibrillation shocks delivered to out-of-hospital sudden cardiac arrest patients

OBJECTIVE

Following out-of-hospital defibrillation attempts, electrocardiographic instability challenges accurate assessment of defibrillation efficacy and post-shock rhythm. Presently, there is no precise definition of defibrillation efficacy in the out-of-hospital setting that is consistently used. The objective of this study was to characterize out-of-hospital cardiac arrest rhythms following low-energy biphasic and high-energy monophasic shocks in order to precisely define defibrillation efficacy and establish uniform criteria for the evaluation of shock performance.

METHODS

Automatic external defibrillators (AEDs) delivering 150 J impedance-compensating biphasic or 200-360 J monophasic damped sine waveform shocks were observed in a combined police and paramedic program. ECGs from 29 biphasic patients and 87 monophasic patients were classified as organized, asystole or VF at post-shock times of 3, 5, 10, 20 and 60 s.

RESULTS

Post-shock time (P<0.0001) and shock waveform type (P = 0.02) affected the classification of post-shock rhythm. At each analysis time, there were more patients in VF following high-energy monophasic shocks than following 150 J biphasic shocks (P<0.0001). The percentage of patients in VF increased with post-shock time. The rate of VF recurrence was not a function of shock type, indicating that refibrillation is largely a function of the patient's underlying cardiac disease.

CONCLUSION

Defibrillation should uniformly be defined as termination of VF for a minimum of 5-s after shock delivery. Rhythms should be reported at 5-s after shock delivery to assess early effects of the defibrillation shock and at 60-s after shock delivery to assess the interaction of the defibrillation therapy and factors such as post-shock myocardial dysfunction and the patient's underlying cardiac disease.

Exercising with diabetes: tips, strategies, and precautions

If you have diabetes, one of the best things you can do for yourself is to stay-or begin to be-active. A regular exercise program can help stabilize your blood sugar, reduce your need for insulin and medication, and keep your weight under control. Diabetes increases the risk of heart disease, but exercise can lower it. Best of all, exercise helps you get more out of life.

Exercise in diabetes management: maximizing benefits, controlling risks

Exercise is a recommended component of diabetes management. In both type 1 and type 2 diabetes mellitus, exercise can increase insulin sensitivity, lower blood glucose, and have positive psychological effects. More markedly in type 2 than in type 1, regular physical activity improves glycemic control, reduces hypertension, and normalizes lipids. Adjustments in insulin dosage, careful blood glucose monitoring, and attention to diet around the time of exercise will help prevent hypoglycemia and hyperglycemia, which are common hazards of exercise in type 1 diabetes. Special precautions are necessary for those who have diabetic complications such as retinopathy or peripheral neuropathy.

Refining and blending of aviation turbine fuels

Aviation turbine fuels (jet fuels) are similar to other petroleum products that have a boiling range of approximately 300F to 550F. Kerosene and No.1 grades of fuel oil, diesel fuel, and gas turbine oil share many similar physical and chemical properties with jet fuel. The similarity among these products should allow toxicology data on one material to be extrapolated to the others. Refineries in the USA manufacture jet fuel to meet industry standard specifications. Civilian aircraft primarily use Jet A or Jet A-1 fuel as defined by ASTM D 1655. Military aircraft use JP-5 or JP-8 fuel as defined by MIL-T-5624R or MIL-T-83133D respectively. The freezing point and flash point are the principle differences between the finished fuels. Common refinery processes that produce jet fuel include distillation, caustic treatment, hydrotreating, and hydrocracking. Each of these refining processes may be the final step to produce jet fuel. Sometimes blending of two or more of these refinery process streams are needed to produce jet fuel that meets the desired specifications. Chemical additives allowed for use in jet fuel are also defined in the product specifications. In many cases, the customer rather than the refinery will put additives into the fuel to meet their specific storage or flight condition requirements.

RT-PCR quantification of AHR, ARNT, GR, and CYP1A1 mRNA in craniofacial tissues of embryonic mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin and hydrocortisone

C57BL/6N mouse embryos exposed to hydrocortisone (HC) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) develop cleft palate. An interaction between these agents produces clefts at doses which alone are not teratogenic. The glucocorticoid receptor (GR) and dioxin receptor (AhR) mediated these responses and their gene expression was altered by TCDD and/or HC in palates examined on gestation day (GD) 14 by Northern blot analysis and in situ hybridization. The present study quantifies AhR, AhR nuclear translocator (ARNT), and GR mRNA at 4, 12, 24, and 48 h after exposure (time 0 = dose administration at 8 A.M. on gestation day 12) on GD12 to TCDD (24 micrograms/kg), HC (100 mg/kg) or HC (25 mg/kg) + TCDD (3 micrograms/kg). The induction of CYP1A1 mRNA was also quantified at 2, 4, 6, 12, 24, and 48 h for control and TCDD-exposed samples. Total RNA was prepared from midfacial tissue of 4-6 embryos/litter at each time and dose. An RNA internal standard (IS) for each gene was synthesized, which included the gene's primer sequences separated by a pUC19 plasmid sequence. Reverse transcription-polymerase chain reaction (RT-PCR) was performed on total RNA + IS using a range of 5-7 IS concentrations across a constant level of total RNA. PCR products were separated in gels (mRNA and IS-amplified sequences differed by 30-50 bases), ethidium bromide-stained, imaged (Hamamatsu Photonics Systems, Bridgewater, NJ), and quantified with NIH Image. CYP1A1 mRNA was significantly induced in the TCDD-exposed samples at all time points examined (p = 0.005 at 2 h and 0.001 after 2 h). During palatal shelf outgrowth on GD12, AhR mRNA levels increased significantly and this was not affected by treatment with TCDD or HC + TCDD. A significant increase in GR was detected at 24 h (p < 0.05) and this was unaffected by any of the exposures. Expression of ARNT increased at 12 h (p < 0.001); however, treatment with HC or HC + TCDD blocked this increase (p < 0.05). At 24 h, the TCDD-treated embryos had significantly lower ARNT mRNA compared with controls (p < 0.001). The relative overall expression level of the genes was AhR > ARNT > GR. Within individuals, expression of AhR and/or ARNT was highly correlated with GR level. In conclusion, CYP1A1 mRNA was expressed in developing craniofacial tissue and was highly induced by TCDD exposure. AhR, ARNT, and GR mRNA are upregulated in early palatogenesis, although not on the same schedule. The TCDD-induced decrease in ARNT at 24 h after dosing and the HC and HC + TCDD-induced delay in upregulation of ARNT may affect the dynamics of heterodimer formation between AhR and ARNT. The changes in ARNT mRNA level could also affect availability of this transcriptional regulator to interact with other potential partners, and these effects, separately or in combination, may be involved in disruption of normal embryonic development.